Field
Embodiments disclosed herein relate to forming magnetic tunnel junctions, and more specifically to forming ultra-smooth bottom electrode surfaces for depositing magnetic tunnel junctions thereon.
Description of the Related Art
Magnetic tunnel junction (MTJ) stacks are typically deposited over bottom electrodes. Conventional sequences include forming bottom electrodes over bottom vias using a damascene process. Oxide is deposited over the bottom vias and then patterned to form openings for the bottom electrodes. Metal is then deposited in the openings to form the bottom electrodes. Chemical Mechanical Polishing (CMP) is used to polish the upper surface of the bottom electrodes back to the upper surface of the oxide. A bottom electrode touch-up layer is then deposited over the bottom electrode and oxide and polished.
One problem with the damascene process is that a step is formed when polishing the bottom electrode material using CMP. This step at the interface of the oxide and the bottom electrode is detrimental to the performance of the MTJ. Additionally, the bottom electrode touch-up layer must be deposited at a greater thickness than desired to accommodate the difficulty in controlling CMP of that layer. This increased thickness of the bottom electrode touch-up layer additionally adversely affects the etching process used to form the MTJs. Still further, the increased thickness of the bottom electrode touch-up layer requires that the MTJ size needs to be bigger than the bottom electrode pad to avoid excessive exposure of the bottom electrode material during an MTJ etch.
Therefore, there is a need for a process to form an ultra-smooth bottom electrode surface for depositing MTJs thereon.